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Wednesday, 10 July 2013

SQL – Structured Query Language for Database quering

Right now I am assuming that the readers are well aware of what Database
means because I would be talking about SQL - a language used to
interact with databases. The database in focus will be Oracle.

In Oracle, the SQL is divided into two basic groups: data definition
language (DDL) or data manipulation language (DML). DDL is used to
define objects within the database just as creating tables or indexes.
DML is used to insert, update and delete data in the database. Finally,
there is data retrieval, which is the SELECT statement.

Oracle makes use of SQL*Plus (SQL Star Plus) as the command line
interface to the let user interact with Database. In a nutshell,
SQL*Plus connects to the database, takes user SQL in and displays
results to user.

The login format is:

"username/password@db_service_name"

The db_service_name is looked up in the TNSNAMES.ora file located in
ORACLE_HOME > network > admin > tnsnames.ora - which will be
provided by the DBA (administrator).

Please note that SQL*Plus places each command into a buffer (opened as
"ed"). You can edit the SQL*Plus buffer, but it is more efficient to
create and run database scripts instead. Re-execute an immediately
previous command by "/".

Before we look into each and every statement, here are some general points about SQL statements to conclude this post:

SQL is not case sensitive

Formatting and indentation only makes it readable to us humans. It makes no difference to servers in any aspect

Database metadata - data about data - like table names, index
names, etc are stored in UPPER case. Use data is stored just how it is
entered